Take a moment and think about what you have done today. Have you repeated the same things that you did yesterday or some other day? Have you done the same things as yesterday but in a slightly different manner? Have you accomplished something completely different that you have never done before? When you think about it, everything in life is a repetition, variation, or contrast.
At the beginning of a musical composition an idea is presented. From that point onward everything is either a repetition of that idea, a variation of it, or a complete contrast to it. Repetition is important because it helps hold the music together. A melody is often repeated so that it stays in the memory and makes better sense in our minds. Variation is a repeat of an idea with some alteration. Those alterations may occur with slight changes in rhythm, melody, or harmony. Contrast is a complete change from anything else that has been played in the music. It adds interest to music because pieces that consist of one repeated idea can be very boring.
Recognizing the repetition, variation, and contrast in a piece of music helps us understand its form. Form is simply the structure of a piece of music. Strophic form is the simplest example of form in music. It is found in most popular music, folk music, hymns, and Christmas songs. Strophic form consists of one melody that is written for several stanzas of poetry. Even when the words change, the music stays the same.
Many compositions, like symphonies, sonatas, and concertos, are broken down into movements. A movement is a large section within an even larger piece of music. Most symphonies have four separate movements that usually can stand on their own as independent works. Each movement has its own form.
The main forms in classical music are theme and variations, rondo, and sonata form. Theme and variations, like the name suggests, has a main theme that is followed by sections that have some variation on it. Each of the sections can alter the melody, harmony, rhythm, or orchestration. For example, one variation may feature the violins, while the oboe plays the next variation. Sometimes the theme will be presented in a major key and a variation will be played in a minor key. There is no limit to the number of variations in this form. Rhapsody on a Theme of Paganini, by Sergei Rachmaninoff (1873-1943), has twenty-four variations.
Capital letters are used to represent sections in some forms. Many songs have a form of ABA, which means the first section — A — is followed by a contrasting section — B. The A section then comes back to conclude the piece. A simple example of ABA form occurs in Twinkle, Twinkle, Little Star. The A section is “Twinkle, twinkle, little star, how I wonder what you are.” The B section is “Up above the world so high, like a diamond in the sky.” And the last A section repeats the beginning. The sections in classical forms are usually much longer than this simple song. Please do not mock Twinkle, Twinkle, though — it was good enough for Mozart to write a theme and variations based on it’s melody.
Rondo form has a main section (A) that is alternated with contrasting ideas. The A section always comes back after the contrasting sections and it concludes the piece. There are several structural possibilities in rondo form. Some have an order of ABABA. Some are ABACABA. It is also possible to have a form of ABACADA, with each letter representing a different musical idea.
Sonata is the name given to pieces of music that feature a solo instrument or a solo instrument with piano. Sonata form is a particular structure of a piece of music. This form was created and refined during the classical era (1750-1820). There are three main sections in sonata form — the exposition, development, and recapitulation. The exposition presents the melodic material of a composition and the development, as you might guess from its name, develops those ideas. The recapitulation repeats the music of the exposition.